Potable water systems are comprised of numerous components including pipe and plumbing fixtures such as faucets, valves, couplings, and pumps which both store and transport water. These components have traditionally been made of copper-based cast and wrought alloys with lead dispersed therein in amounts between 1-9% by weight. The lead allows these components to be more easily machined into a final product which has both a predetermined shape yet acceptable strength and watertight properties.
The lead used to improve the machinability of these copper alloy materials has been proven to be harmful to humans when consumed as a result of the lead leaching into potable water. This damage is particularly pronounced in children with developing neural systems. To reduce the risk of exposure to lead, federal and state governments now regulate the lead content in potable water by requiring reductions in the amount of lead which can leach from plumbing fixtures. A variety of strategies have been developed to address this problem. For example, simply reducing the amount of lead in plumbing fixtures has been attempted. However, such low lead content alloys are difficult to machine.
Another strategy is to develop specific alloys such as that disclosed in U.S. Pat. No. 4,879,094 to Rushton. The patent describes an alloy which contains 1.5-7% bismuth, 5-15% zinc, about 1-12% tin and the balance copper. This copper alloy is capable of being machined, but must be cast and not wrought. This is undesirable since a wrought alloy may be extruded or otherwise mechanically formed into shape. It is thus not necessary to cast objects to a near finished shape. Further, wrought alloy feed stock is more amenable to high speed manufacturing techniques and generally has lower associated fabrication costs than cast alloys.
A copper based machinable alloy with a reduced lead content or which may be lead free was disclosed by McDivitt in U.S. Pat. No. 5,137,685. This alloy contains from about 30-58% by weight zinc, 0-5% weight of bismuth, and the balance of the alloy being copper. This alloy is expensive to produce, however, based both on the cost of the bismuth as compared to lead, and further since the bismuth must be thoroughly mixed within the matrix of the copper alloy material.
Another approach to inhibiting lead leaching in water involves non-continuous coating of lead dispersoids in the brass fixture as described by Coltrinari et al. in U.S. Pat. No. 5,544,859. The patent describes a method and apparatus for selectively coating lead dispersoids with, e.g., tin or bismuth, thereby reducing the amount of lead exposed to the liquid conduit. This coating results in lower lead leaching into the liquid.
Yet another approach involves treating brass plumbing components with an aqueous solution containing a desired concentration of chloride and pyrophosphate as described by Downey in U.S. Pat. No. 5,454,876. The patent discloses a method for promoting dissolution of lead by chlorine ion and sequestering the dissolved lead in the solution by pyrophosphate ion to prevent the lead dissolution reaction from reaching equilibrium. This process generates a waste solution which cannot be simply discarded but requires special disposal methods.
Therefore, despite the developments made in the area of reduced lead leaching into potable water systems, there remains a need to provide a material which is less susceptible to leaching lead into potable water systems, yet which utilizes the inherent benefits of copper alloys that contain lead, and for a process of removing lead from brass fixtures which does not generate wastes that require special disposal methods.